Utilities provide electrical power to consumers in response to demand. The total amount of electricity provided to consumers at any given time changes based on various factors, such as environmental conditions and time of day. For example, consumers may require large amounts of electricity to run air conditioning systems on a hot summer afternoon. Utilities may have difficulty supplying enough electricity to meet the demand during peak hours. As a result, consumers may be charged a higher rate for electricity use during peak hours than during off-peak hours.
Consumers typically have little information about the amount of power they consume. The consumer's electric utility may provide the consumer with a monthly bill that indicates the total amount of power consumed during the month, as measured by the utility meter. Unfortunately, the consumer does not have access to more detailed information about their power usage, such as the amount of power consumed by various devices within the home. Although power meters are available for measuring the power consumed by a single device at a given time, the user may need to manually plug the power meter into the device's electrical connection to make the measurement. Manually connecting the power meter to individual devices may take a significant amount of time and can lead to a complicated and costly set of measurement devices.
Various advantages are possible if more information is made available about consumers' power usage. As an example, consumers may learn which of their devices consume the most power, enabling the consumer to turn off these devices at appropriate times to reduce costs and/or conserve energy. A smart electrical grid or “Smart Grid” has been proposed that may take advantage of power-related information to provide a more flexible power infrastructure with various advantages. A barrier to implementing such a system is the present difficulty of measuring the power usage of individual devices or groups of devices.
Non-Intrusive Load Monitoring (NILM) is an approach to electrical system diagnostics and power monitoring that can employ a smaller number of sensors than other device-specific monitoring systems. A NILM system can identify and monitor individual loads on a power distribution system by measuring the frequency content of transient events in the current signals. Such monitoring may be performed from a centralized remote location. According to conventional techniques, the current signal is measured using a magnetic field sensor wrapped around the utility feed of the subsystem to be monitored. However, such a sensor may be impractical for some applications. A wrap-around sensor cannot be used when placed around both the Line and Neutral wires in the home because the sensor would measure a current of zero due to the flow of identical current in opposite directions. Using a wrap-around sensor to monitor power in the home may be expensive because skilled labor would be needed to separate the Line and Neutral wires so that the wrap-around magnetic field sensor can be placed around only one of the wires.